Commercial baking ovens include a large enclosed chamber with a continuous conveyor that conveys products to be baked through an oven inlet and conveys baked product through an oven outlet. The conveyor moves continuously. Additional product to be baked is added to keep the conveyor loaded at the inlet end. These ovens often have multiple zones. The oven temperature may change from one zone to the next. Each zone can employ several burners that extend from one side wall to another side wall and transverse to the direction of movement of product moving on the continuous conveyor.
The burners have a length that depends on the width of the continuous conveyor and the distance between the oven side walls. Large baking ovens may have burners that are more than sixteen feet long. The fuel burned by the burners may be natural gas, propane, butane or other combustible gases.
Product being baked midway between a near side and a far side of the continuous conveyor must be baked to the same extent as the product on both sides of the continuous conveyor. Product must be fully baked in the center and not over baked on bottom or top surfaces. Product that is over heated and darkened excessively is discarded.
Each burner, in a typical baking oven, has a burner tube. The burner tube has a gas receiving end that is anchored to a first sidewall of the oven. The tube has a tube slot on one side that extends at least the width of the conveyor. Gas passes through the slot and burns outside the tube adjacent to the slot. The heat produced by the burning gas heats the burner tube. The length of the burner tube increases as the temperature increases. The length of the burner tube decreases as the temperature decreases. The slot in the side of the burner tube weakens the slot side, of the burner tube. This weakened side of the burner tube expands pipe length more than the closed side as pipe temperature increases. The increased length of the slot side bows the burner tube about a vertical or substantially vertical axis. The free end of the burner tube adjacent to a second side wall of the oven is supported by a horizontal support beam. The horizontal support beam permits movement of the free end of the burner tube due to changes in tube length and due to bowing about a substantially vertical axis as a result of temperature changes in the burner tube. The free end of the burner tube extends to a position between second side wall and the continuous conveyor. The burner tube is also positioned below an upper run of the continuous conveyor and above a lower run of the continuous conveyor.
To obtain ideal product quality, baking ovens to have been equipped with control systems that adjust fuel flow rates, turn burners off and relight burners to obtain high quality baked products. Igniters employed in ovens have been introduced that control the distance between electrodes which create a spark and control the location of a spark relative to and a fuel port of a burner tube. Maintaining the spark gap distance and the position of the sparks relative to a burner is difficult. Burners move due to temperature changes. Igniter parts expand and contract due to temperature changes. Igniter parts have failed due to temperature changes over a period of time and failed to ignite a gas.
Failure of an igniter to ignite a burner results in the control system discontinuing the flow of fuel to the burner to prevent a possible explosion. Inspection and adjustment or repair of an igniter cannot take place in most ovens until unbaked and partially baked product is removed and the oven cools. The cost of lost product may be substantial. The down time and the cost of heating a cold oven can also be significant.
Igniters, that are currently used in baking ovens, have an outboard end that extends through the first oven wall and is pivotally supported by the oven wall. An inboard end of the igniter is supported by the burner tube. The igniters have an elongated tube that is parallel to the burner tube. The elongated igniter tube extends some distance into the oven to reach a position adjacent to the tube slot where combustion can be initiated. Some of these igniters work well. Other igniters do not work well. They generally require frequent maintenance and adjustment. The igniters used today are relatively long so that they can extend through the first side wall and into a position to ignite gas. Igniters employed in baking ovens are expensive due to their size, weight, and the need to accommodate movement of a burner in response to oven temperature changes.